1. Field of the Invention
The present invention relates to a bobbin housing assembly in a sewing machine having at least one hook, and a tension spring which rests against the bobbin housing, and advantageously relates to a lockstitch sewing machine of this type.
2. Description of Related Art
A lockstitch sewing machine having a hook, a bobbin housing assembly which includes the hook, and a spring bar, is disclosed in Federal Republic of Germany Patent 34 46 547, having a U.S. counterpart U.S. Pat. No. 4,691,650. In this device, the spring bar rests against the bobbin housing. The spring bar is fastened to a carrier which, in turn, is fastened to the base plate of the lockstitch sewing machine. The carrier furthermore has two cams which are arranged essentially in the center region of the loop press-off side of the bobbin housing and which receive the spring bar between them. The obliquely directed spring bar assumes a position with respect to the cam which is towards the rear in the direction of rotation of the hook body, so that a larger clearance is always present between the free end of the spring bar and the surface of the rear cam facing it.
This device has the following disadvantage. In a lockstitch sewing machine operating with a high stitching rate, the spring bar begins to oscillate, and as a result, the position of the bobbin housing, which itself is held by the spring bar, becomes unstable. As a result of this, defects can arise in the sewing.
Another lockstitch sewing machine having a hook and a spring bar resting against the bobbin housing is disclosed in Federal Republic of Germany Patent 26 16 738, having U.S. counterpart U.S. Pat. No. 4,137,858. In this device, the bobbin housing has a holding finger which is received by two stops provided on a bottom side of the throat plate of the lockstitch sewing machine. Because of the relatively narrow passage clearances between the two stops and the holding finger, passage of the loop of the needle thread (top thread) can be impeded. Furthermore, the manner of operation of this spring bar is also not substantially vibration-free.